Miniature pan/tilt tracking mount

ABSTRACT

The invention is directed to a computer-controlled miniature pan/tilt tracking mount for the precise control of position, velocity, and acceleration of small payloads (e.g., a video camera). The invention consists of a motorized rotational tilt axis mounted atop a motorized rotational pan axis. For both axes, a worm gear mounted upon the motor shaft bidirectionally rotates a worm wheel mounted upon the orthogonal load axis shaft. A large ratio of motor size to armature weight provides high relative torque, speed, and accuracy. The worm gears provide compact reduction with minimal backlash and they can hold position without energized motors to conserve power for battery-operated uses. The invention includes integrated motor drive power electronics and microcontroller execution of host computer commands to effect precise control of pan/tilt mount speed, acceleration, position, configuration, and motor and electronics power consumption. Superior motor drive capabilities are achieved by the use of pulse-width modulation (PWM).

This application is a continuation of application Ser. No. 08/549,912,filed Oct. 30, 1995, abandoned, which was a divisional application ofapplication Ser. No. 08/449,257, filed May 25, 1995, which issued asU.S. Pat. No. 5,463,432 on Oct. 31, 1995, which was a continuation ofapplication Ser. No. 08/066,672, filed on May 24, 1993, abandoned.

FIELD OF THE INVENTION

The invention relates to a miniature motorized apparatus, known as apan/tilt tracking mount, that provides for precise and high-speedrotation and tilting of mounted payloads in response to host computergenerated commands.

BACKGROUND OF THE INVENTION

Highly accurate and fast computer-controlled pan/tilt mounts have beenused in the field of tracking for decades (e.g., for missile trackingU.S. Pat. No. 3,559,937, target tracking, weapon/gun mount). Trackingmounts provide for precise and fast computer control of pan/tiltposition, speed and acceleration. These tracking mounts have beenintrinsically complex and costly since they typically carry largepayloads (e.g., greater than 20 pounds), and they position with greataccuracy (e.g., 1 second arc) and speed (e.g,. over 300°/second). Thepresent pan/tilt tracking mount invention provides a hithertounavailable capability for applications that have small payloads (e.g.,less than 10 pounds) and which require a miniature and compact mountthat can be simply controlled, and is particularly well-suited for lowcost manufacture.

Recent advances in the fields of image processing, computer vision androbot vision have shown that active control of sensor pan/tilt positioncan facilitate and simplify computations that support a wider range ofactivity than a passive sensor. Advances in low cost and powerfuldigital signal processors (DSP), accurate and miniature solid statecameras, sensor processing algorithms, and robotics have madesensor-based control of pan/tilt position applicable to a wide range ofuses, though the lack of a suitable, low cost pan/tilt mount hasretarded advancements in related fields and applications. The inventiondisclosed herein provides the necessary tracking mount capabilitieshitherto unavailable to these fields.

Motorized pan/tilt mounts have achieved widespread use in the fields ofsurveillance and security (e.g., U.S. Pat. Nos. 4,673,268 and4,937,675). Often used outdoors or under harsh conditions, these mountsare often liquid-proof. These pan/tilt mounts typically achieve mediumto large payload capacity with small motors by the use of largemechanical speed reductions, thus, they are generally too slow for mosttracking applications. Though pulse-width modulation (PWM) andconstant-current motor drivers achieve better motor performance (e.g.,better acceleration, higher switching rate, better dynamic torque), mostprior art security motor drivers use simpler voltage drivers due totheir simplicity and historically lower cost, though advances in singlechip, high-power microelectronics have made PWM constant-current driveseconomically competitive. Precision is not typically inherent in theprior art designs, since their mechanical speed reductions arefrequently subject to backlash (e.g., as from spur gear trains),slippage (e.g., as from belt drives), and other mechanical effects.Small solid-state cameras have created a need for miniature mounts,since unobtrusiveness is desirable for surveillance and security, thoughcurrent mounts are still considerably larger than their cameras, andthey are not well-suited for miniature and ultraminiature realization.In addition, human and very simple automated pan/tilt controls in theprior art (e.g., joystick operation, or fixed scanning and positionpresets) are not generally amenable to integrated computer control ofmount position in response to changes in sensor input. The pan/tiltinvention disclosed herein provides hitherto unavailable capabilities inthe surveillance and security fields due to its integrated computercontrol suitability for miniaturization/ultraminiaturization and lowcost manufacture, it does not impose an upright mounting requirement(e.g., it can be mounted upside down from the ceiling for storesurveillance), and its advanced tracking mount features (e.g., speed,precision, computer-control) facilitate novel surveillance and securitystrategies for control and computation.

SUMMARY OF THE INVENTION

The present invention is a miniature pan/tilt tracking mount for smallpayloads (e.g., less than 10 pounds) that provides capabilities notavailable in prior art in terms of its miniature size (e.g.,2.98"×5.13"×3.55"), positional accuracy (e.g., 3 minutes arc), highspeed (e.g., slew rates over 300°/second), precise control of speed andacceleration, suitability for liquid resistant realization, gravityindependent mounting (e.g., it can be mounted upside-down), integratedmicroprocessor control and interface, and particular suitability for lowcost manufacture. The invention consists of a motorized rotational tiltaxis mounted atop a motorized rotational pan axis. For both axes, a wormgear mounted upon the motor shaft bidirectionally rotates a worm wheelmounted upon the orthogonal load axis shaft. An advantage over the priorart is provided by the invention's small size and its high relativetorque, speed, and accuracy that are achieved by a large ratio of motorsize to armature weight, and the use of a single worm gear per axis thatprovides compact and flexible reduction while providing minimal backlashand the ability to hold position without energized motors to conservepower for battery-operated uses (i.e., worm pressure angles can beselected to prevent gear backdriving).

The invention includes motor drive power electronics and microcontrollerexecution of host computer commands to effect precise control ofpan/tilt mount speed, acceleration, position, and configuration. Uponreset, the microcontroller precisely moves the mount to a repeatable andknown "home" position using electrical sensor feedback from the mount(e.g., limit switch, encoder feedback). Precise motor rotation relativeto the home position is maintained by the microcontroller (e.g., by stepcount for open-loop stepper control, or, incremental encoder feedbackfor closed-loop stepper or DC servomotor control). Superior motor drivecapabilities are achieved by the use of pulse-width modulation (PWM) andconstant current driving of motor windings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevated perspective view of an embodiment of thepan/tilt mount invention.

FIG. 2 shows a detailed cross-sectional front view of an embodiment ofthe pan/tilt mount invention.

FIG. 3 shows a block schematic of the major functional pan/tilt mountcontroller components and connections.

DETAILED DESCRIPTION

FIG. 1 shows an elevated perspective view of a preferred embodiment ofthe pan/tilt mount invention. The mount consists of a tilt assembly 10mounted atop a pan assembly 11. A payload (e.g., a camera) secured tothe load mounting plate 12 is rotated by the tilt assembly 10 and itstilt motor 19 through a tilt angle TA of at least 100 degrees. The tiltassembly 10 is rotated by the pan assembly 11 and its pan motor 20through a pan angle PA. When a tilt assembly cable 16 is used toelectrically connect the tilt assembly 10 to the pan assembly 11, thepan angle PA is at least 330 degrees. In an alternative embodiment, thetilt assembly cable 16 may be replaced with a pancake slip ring (e.g.,model 1062 from Fabricast Incorporated or model SR2300 from MaureyInstrument Corporation) mounted upon the pan axis shaft 35 between thetilt housing 17 and pan housing 15, in which case the pan angle PA hasunlimited rotation through a full 360 degrees. Knobs 46 47 mounted onthe motor shafts provide for manual operation of the mount. All pan/tiltmount electrical connections terminate in an electrical connector 13mounted within a connector housing 14 that is secured to the pan housing15. A control cable 18 electrically connects the pan/tilt mount to thecontroller to be detailed hereinafter. Threaded mounting holes (notshown) in the pan housing 15 provide for bottom or front mounting to asupport (e.g., tripod, robot).

FIG. 2 shows a detailed cross-sectional front view of an embodiment ofthe pan/tilt mount. A standard camera #1/4-20 load mounting bolt 24 isprovided to secure a payload (e.g., video camera) to the load mountingplate 12. The mounting plate 12 is secured to the left tilt bracket 21and right tilt bracket 22 by retaining screws 23 inserted throughrecessed loose fit holes in the mount plate 12 that allow for minoradjustment of tilt bracket 21 22 spacing. The retaining screws 23 may beremoved to customize the load mounting plate 12. The right tilt bracket22 is secured to the tilt axis shaft 25 (e.g., by a shaft pin). The lefttilt bracket 21 is slotted (not shown) to form a clamp secured to thetilt shaft 25 by the tightening of a clamp screw 26 in order to providefor tilt shaft 25 removal and tilt bracket 21 22 spacing adjustment. Thetilt shaft 25 is supported by two flanged bearings 27 28, ball bearingsin a preferred embodiment, that are recessed into the tilt housing 17.Resistance against liquid and contaminants is enhanced by the use ofshielded bearings and O-rings between the left 21 and right 22 bracketsand the tilt housing 17. In a preferred embodiment, a tilt axis tensionadjustment screw and washer 29 threaded into the axial center of thetilt axis shaft 25 precisely adjusts the tilt bracket 21 22 spacing toachieve bearing 27 28 preloading and tilt mount rigidity prior to thetightening of the clamp screw 26 and mount plate screws 23. A worm wheel30 secured to the tilt axis shaft 25 engages a worm gear 31 secured tothe tilt motor shaft 32. The tilt motor 19 is secured to the tilthousing 17 by retaining screws inserted through loose fit holes (notshown) that allow for minor adjustment to achieve tight engagement ofthe worm wheel 30 and gear 31. A cover 33 is secured to the tilt housing17 to protect internal mechanisms from contaminants and liquids. Asshown in FIG. 1, mechanical stop pegs 45 can be inserted into the tilthousing 17 which engage the right tilt bracket 22 to avoid tilt anglesTA that interfere with the pan motor 20.

As shown in FIG. 2, the tilt assembly 10 is secured to the pan axisshaft 35 by two opposing set screws 34 inserted in the tilt housing 17.The pan shaft 35 is supported by a flanged 36 and plain 37 bearing, ballbearings in a preferred embodiment, that are recessed into the panhousing 15. A shaft retaining clip 38 secures one end of the pan shaft35, both of which are recessed with the plain bearing 37 to facilitatemounting to the pan housing 15 bottom. Resistance against liquids andcontaminants is enhanced by the use of shielded bearings, an O-ring (notshown) between the tilt 17 and pan 15 housings, and sealing (e.g., bymetal tape) of the recessed plain bearing 37 and retaining clip 38. Thepan axis drive is analogous to the tilt axis drive. A worm wheel 39secured to the pan axis shaft 35 engages a worm gear 40 secured to thepan motor shaft 35. As for the tilt axis, loose fit motor mount screwholes (not shown) provide for worm wheel 39 and gear 40 tensioning. Whena tilt assembly cable 16 is used, rather than a slip ring as describedearlier, a pan mechanical stop (not shown) is desirable to avoid cabledamage. A mechanical pan axis stop is simply realized by inserting adowel pin into the bottom front center of the tilt housing 17 andanother opposing dowel pin is inserted into the top back center of thepan housing 15, such that these pins are inserted at the same radiusabout the pan shaft 41, and the exposed pins engage one another withoutcontacting the opposing assembly housing. A cover 41 secured to the panhousing 15 protects against contaminants and liquids.

The motor and mount position sensor embodiment employs stepping motorsand precision limit switches to accurately and repeatably controlpan/tilt mount position. Limit positions are detected by the use ofvanes 43 44 mounted with each worm wheel 30 39 that interrupts a lightbeam in a slotted optical limit switch 42. High limit position accuracyand repeatability is achieved by the use of a transmissive photoIC(e.g., Omron EE-SX493) possessing a narrow slot (e.g., 2 mm), narrowaperture (e.g., 0.2 mm), precise voltage control, thermal correction,and a Schmitt switching circuit. In this configuration, each motor canbe stepped open-loop relative to the established mount home positions.This embodiment provides for low cost manufacture by omitting the needfor more expensive encoders and drive controls.

To avoid classical problems associated with open-loop motor control, analternative embodiment can include encoders to establish closed-loopmotor control. This embodiment uses dual shaft motors to allow simplemounting of motor shaft encoders (e.g., an incremental opticalquadrature encoder such as the HP HEDS-5500). Mechanical stops can bedetected by the encoders as motor stalls and the limit switches 42 andvanes 43 44 can be omitted, though the preferred embodiment retains themfor added safety and flexibility. Another alternative embodiment, thoughusually substantially more expensive, can replace the stepping motorswith encoders and DC servomotor controls to achieve higher motor torqueto weight ratios and better dynamic torque characteristics. Because DCmotors generally have smaller diameters than comparable stepping motors,and the overall pan/tilt mount dimensions are substantially affected bymotor diameter, DC motors can provide a substantially more compactembodiment.

FIG. 3 shows a block schematic of the major functional pan/tilt mountcontroller 50 components and connections. A pan motor driver 51energizes the pan motor 20 and a tilt motor driver 52 energizes the tiltmotor 19. A microcontroller 53 executing a firmware program 54 controlsmotor drivers 51 52, processes pan 59 and tilt position sensor 60 input,host computer 55 command execution and feedback, and communications witha controller network 56. Input power conditioning 58 filters the inputfrom a DC source 57 and supplies pan motor power V_(p), tilt motor powerV_(t), and logic power V_(cc).

In the current embodiment, which uses stepping motors as describedearlier, a single chip power IC (UDN2917EB) is used for each axis driver51 52. These compact drivers incorporate a dual full bridge driver,pulse-width modulation (PWM), current sensing for constant currentdriving, digital control providing four level current control, voltagereference control of current, internal parasitic diodes, high currentand voltage capacity, and thermal protection shutdown. PWM is thepreferred motor driving technique since it provides for superior motorand driver performance, efficient control of current consumption, and itcan accept a wide range of input voltages (e.g., 11-45VDC) that providesfor flexible DC power source 57 selection which allows simpler and moreeconomical installation. Digital control of current level is used todecrease winding current to achieve more consistent motor torque forhalf-steps in which multiple windings are simultaneously energized, andcurrent level can be controlled by host computer 55 commands that allowuser programs to conserve mount power consumption (e.g., as inbattery-operated applications). In an alternative embodiment, a digitalto analog converter can be used by the microcontroller 53 to adjust thevoltage reference control of current, thereby providing formicrostepping in order to provide higher rotational resolution andreduce motor cogging. As discussed earlier, an alternative embodimentcan use DC servomotors in place of stepping motors. In this case, themicrocontroller 53 can implement servocontrol in its firmware program 54using a single UDN2917EB power driver chip above-described with theaddition of motor shaft position encoder input 59 60. Alternatively,simpler firmware 54 and improved motor performance may be achieved athigher cost by the use of highly integrated DC servomotor control chipsas replacement PWM drivers 51 52 (e.g., the HP HCTL-1100).

In the current embodiment, an MC68HC11-based microcontroller S3 fromCoactive Aesthetics in San Francisco, Calif. (model GCB11) was used. Thefirmware program 54 digitally controls the motor drivers 51 52, performsmount initialization and homing, processes host computer 55 commands andfeedback via an RS-232 port, and capability is provided for command andfeedback via an RS-485 multidrop controller network 56. When input DCpower 57 is applied, the program 54 performs a system reset byinitializing internal data structures, verifying mount defaults storedin its EEPROM, commanding the motors to move until the limit positionsare identified, and moving the mount to its home position. The program54 processes commands from and returns status to the host computer 55 orcontroller network 56 for mount position, speed, acceleration, upperallowable speed limit, starting motor velocity, unit reset, positionalresolution, position limits, and mount parameter defaults read fromEEPROM upon power up. In addition, commands and queries are provided toallow the control of motor power mode when in-transit and stationary.These modes include high power mode (energized windings at ratedcurrent), regular power mode (full steps use rated winding current, halfsteps use 66% rated winding current), low power mode (windings use 33%of the current used in regular power mode), and when stationary a motorpower off mode is provided. Executed position and speed commandsoverride previous position and speed commands that may not have yetcompleted (i.e., on-the-fly position and speed changes are provided),and an await completion command is provided to allow executing positionand speed commands to complete before new commands are processed. Inaddition, two command execution modes are provided. In immediate mode,position and speed commands are executed immediately. In slaved mode,position and speed are executed upon an await completion command inorder to allow simultaneous commencement of pan and tilt axis commandexecution.

In interactive command mode, pan/tilt mount commands are specified byASCII strings which are well suited for interactive user control from aterminal. Alternatively, a binary command mode is provided to provide amore compact command format that a program executing on the hostcomputer can use to achieve significant improvements in host/controllercommunications bandwidth. For example, binary mode commands typicallyuse less than one third the number of bytes required by the interactiveASCII mode, so a tripling of bandwidth can be obtained (e.g., binarymode on a 9600 baud RS-232 link can achieve command transfer rates thatan interactive ASCII mode would require over 28.8 K baud to achieve).

The program 54 performs interrupt-driven control of motor drivers 5S 52to precisely control pan 20 and tilt 19 motor acceleration,deceleration, velocity, and current levels. As described earlier, thecurrent embodiment uses stepping motors. Each motor has an associatedsoftware routine that is activated by an interrupt generated by themicrocontroller 53 parallel timing circuitry, and this routine controlsits associated motor driver 51 52 to affect motor winding polarity andcurrent, updates motor state variables, and schedules the time at whichthe next interrupt should again activate the routine. These motorroutines run at a higher priority than the main program which processeshost commands and queries in order to achieve precise motor speedcontrol that is independent of host communications traffic. For speedsat or below the starting motor velocity, the stepping motor ishalf-stepped at the commanded velocity until the desired position isattained. For speeds above the starting motor velocity, the motor isaccelerated from the starting velocity to the desired slew rate and thendecelerated to the desired position. For velocities above the startingrate, full steps are used except when a half step is required to startfrom or end at a half-step position. Linear acceleration was used sinceit has low computational requirements (a precomputed table may beindexed to determine step time intervals). Preferred embodiments can usemore computationally intensive acceleration methods that may providebetter dynamic performance (e.g., S-curve acceleration). The currentembodiment, and alternative embodiments described earlier, may usealternative motor controls as are customary and applied.

The following are some exemplary parameters showing pan/tilt performanceand materials for the current embodiment.

Maximum payload: 5 pounds

Maximum velocity: over 300°/second

Resolution: 3.086 arc minutes

Tilt range: greater than 100°

Pan range: greater than 330°

Mount dimensions: 2.98"(width)×5.13"(height)×3.55"(depth)

Pan and tilt motor, Oriental Motor, PK245-01BA 1.8°; 46 oz/in, hybrid2-phase stepping motor

Worm gear reduction: 17.5:1

Motor driver: Allegro Microsystems, UDN2917EB

Dual full H-bridge, PWM constant current bipolar drive

Input Voltage:

Motor power: 11-45VDC unregulated

Logic power: 8-30VDC unregulated (uses internal 5VDC switcherregulator), or, 5VDC regulated

Power Consumption:

Full-power mode: 16 W continuous peak

Low-power mode: 7.5 W continuous peak

Holding power off mode: less than 1 W

The following are some exemplary host computer 55 commands executed bythe firmware program 54 to control pan/tilt mount operation. <axis> isthe character "T" for the tilt axis or the character "P" for the panaxis.

Pan/tilt mount axis commands:

General form: <axis><command><value><delim>→ <status>!

Go to position: <axis>P<position><delim>→ <status>!

Go to offset position: <axis>O<relative position><delim>→ <status>!

Set desired speed: <axis>S<positions/sec><delim>→ <status>!

Set acceleration: <axis>A<positions/sec2><delim>| <status>!

Set speed bounds: <axis> <upper>|<lower>!<positions/sec><delim>→<status>!

Move power mode:<axis>M <hi power>|<reg power><|<lo power>!<delim>→<status>!

Hold (stationery) power mode:<axis>H <reg power>|<lo power>|<poweroff>!<delim>→ <status>!

Queries:

General form: <axis><command><delim>→<query answer>Axis Control Commandsbecome queries when the <value>argument is omitted.

Resolution: <axis>R<delim>→<arc seconds per position>

Position bounds: <axis> <min>|<max>!<delim>→<boundary position>

Unit Commands:

Command menu: ?<delim>→<menu>

Await completion: A<delim>→<status>

Reset unit: R<delim>→ <status>!

Immediate mode: I<delim>→ <status>!

Slaved mode: S<delim>→ <status>!

Defaults used at power up (saved in EEPROM): D <save currentsettings>|<restore prior settings>|<restore factory settings>!<delim>→<status>!

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications. The claims are intended to cover any variations, uses oradaptation of the invention following, in general, the principles of theinvention, and including such departures from the present disclosure ascome within known and customary practice within the art to which theinvention pertains.

I claim:
 1. A method for one or more host computers to dynamicallycontrol and query the precise position, speed, and state of one or morepan/tilt mounts, comprising the steps of:providing a pan/tiltcontroller, including a dedicated embedded processor for executingreal-time pan/tilt control functions and processing of communicationsand commands from said one or more distinct and separate host computers,said embedded pan/tilt controller processor sharing no computationalresources with said one or more host computers; providing a motorizedpan/tilt mount with minimal drivetrain backlash, motors and gearing thatcan precisely rotate the pan and tilt axes over a wide speed andacceleration range, and incorporating pan and tilt limit positiondetection sensors that are precise and highly repeatable; said pan-tiltmount is electrically connected to the pan/tilt controller, regulatingeither the current or voltage to windings of a pan motor and a tiltmotor of said pan/tilt mount using said controller, and said controllerreceiving a set of pan and tilt position sensor feedback signals fromsaid pan/tilt mount; communicating between each of a set of one or morepan/tilt controllers and said one or more host computers, where eachsaid host computer electrically is connected by a standard digitalcommunications interface to provide a bi-directional communications linkto each said pan-tilt controller; wherein each of said one or more hostcomputers can issue command signals to said controller to effect desiredpan/tilt mount movement, and each of said one or more host computers canissue command signals to said one or more controllers to query currentpan/tilt mount movement, position, status, and configuration;calibrating absolute pan and tilt mount positions relative to a pan/tiltmounting point so that absolute pan and tilt positions may be preciselyrepeated; wherein said calibrating step is initiated by at least one ofthe following events: upon power being supplied to said pan-tiltcontroller, upon receiving a calibrate command signal from at least oneof said one or more host computers; setting precisely the absoluterotational speed and direction for pan and tilt movements according to asetting command signal received by said controller from at least one ofsaid one or more host computers such that said controller can preciselyand repeatably position the pan and tilt axes relative to said pan/tiltmounting point; controlling the movements of said pan and tilt mountindependently and concurrently according to signals from at least one ofsaid one or more host computers and the particular pan/tilt controllerof said one or more pan/tilt controllers associated with said pan andtilt mount; parsing and executing incoming host computer commands bysaid one or more controllers concurrent with the execution by saidcontroller of pan-tilt mount movements; and executing position and speedcommand signals received by said pan/tilt controller from one of saidone or more host computers without delay such that said command signalspreempt the instructions of previous position and speed command signalsthat may not have yet completed.
 2. The pan/tilt controller as in claim1, further comprising the step of:controlling the timing of when saidone or more pan/tilt controllers begin executing desired pan/tiltactions to achieve coordinated multiaxis movements by said one of saidone or more host computers.
 3. The pan/tilt controller as in claim 2,further comprising the step of:querying said pan/tilt controller todetermine the current rotational speed and current absolute position ofthe pan and tilt axes even when said pan or tilt movements are inprogress, using said one of said one or more host computers.
 4. Thepan/tilt controller as in claim 3, further comprising the stepof:providing one of said one or more host computers with communicationsfeedback from said pan/tilt controller when a desired pan position hasbeen attained when commanded to provide such communications feedback bysuch a one of said one or more host computers.
 5. The pan/tiltcontroller as in claim 3, further comprising the step of:providing oneof said one or more host computers with communications feedback fromsaid pan/tilt controller when a desired tilt position has been attainedwhen commanded to provide such communications feedback by such a one ofsaid one or more host computers.
 6. The pan/tilt controller as in claim3, further comprising the step of:providing one of said one or more hostcomputers with communications feedback from said pan/tilt controllerwhen a desired pan position and a desired tilt position has beenattained when commanded to provide such communications feedback by sucha one of said one or more host computers.
 7. The pan/tilt controller asin claim 3, further comprising the step of:providing one of said one ormore host computers with communications feedback from said pan/tiltcontroller when a desired pan speed has been attained when commanded toprovide such communications feedback by such a one of said one or morehost computers.
 8. The pan/tilt controller as in claim 3, furthercomprising the step of:providing one of said one or more host computerswith communications feedback from said pan/tilt controller when adesired tilt speed has been attained when commanded to provide suchcommunications feedback by such a one of said one or more hostcomputers.
 9. The pan/tilt controller as in claim 3, further comprisingthe step of:providing one of said one or more host computers withcommunications feedback from said pan/tilt controller when a desired panspeed and a desired tilt speed has been attained when commanded toprovide such communications feedback by such a one of said one or morehost computers.
 10. The pan/tilt controller as in claim 3, furthercomprising the step of:precisely setting of a desired pan and tiltrotational speed as an offset from the current pan or tilt speed by thepan/tilt controller upon receiving a command signal from said one ormore host computers.
 11. The pan/tilt controller as in claim 1, furthercomprising the step of:precisely setting of a desired pan and tiltrotational position as an offset from the current pan or tilt positionby the pan/tilt controller upon receiving a command signal from said oneor more host computers.
 12. The pan/tilt controller as in claim 1,further comprising the steps of:precisely setting of a desired pan andtilt rotational speed as an offset from the current pan or tilt speed bythe pan/tilt controller upon receiving a command signal from said one ormore host computers, and precisely setting of a desired pan and tiltrotational position as an offset from the current pan or tilt positionby the pan/tilt controller upon receiving a command signal from said oneor more host computers.
 13. The pan/tilt controller as in claim 1,further comprising the step of:precisely controlling changes in pan andtilt speed using said pan-tilt controller vary a rate of panacceleration and tilt acceleration, according to command signals fromsaid one or more host computers.
 14. The pan/tilt controller as in claim1, further comprising the step of:varying the current levels applied topan/tilt mount pan motor windings and tilt motor windings by saidpan/tilt controller, according to command signals from said one or morehost computers; wherein the current applied to a stationary pan/tiltmount pan motor winding an be set independent from the current appliedto a pan/tilt mount motor pan motor winding when the pan motor isturning, wherein the current applied to a stationary pan/tilt mount tiltmotor winding can be set independent from the current applied to apan/tilt mount motor tilt motor winding when the tilt motor is turning,and wherein said one or more host computers can command saidpan/tilt/controller to provide different magnitudes of motor windingcurrents to said pan motor and to said tilt motor when said motors arestationary as compared to when said pan and said tilt motors areturning.
 15. The pan/tilt controller as in claim 1, further comprisingthe step of:assigning a unique identifier to each pan/tilt controller,such that a first of said one or more host computers can communicatecommand signals and receive feedback signals from a selected controller,wherein said first of said one or more host computers may broadcastcommand signals to one or more of said one or more pan/tilt controllers.